This application requests funds for the purchase of a Zeiss 10 A electron microscope and a Hewlett Packard digitizer. Within the last five years, the nature of research projects being undertaken within the Department of Biology has changed considerably, and the existing electron microscope facilities are now inadequate. The current programs of the eight research groups listed in this application involve carrying out studies on: 1) genome sequence organization and DNA replication in prokaryotes and eukaryotes; 2) bacterial chromosome structure; 3) the regulation of cellular microtubule assembly; and 4) the development of the immune system. The standard procedures used for such studies include heteroduplex mapping of nucleic acids, high resolution microscopy of protein nucleic-acid complexes, and analyses of microtubule formation and distribution using negative staining, thin sectioning and immunoelectron microscopy. All of these studies require a high resolution electron microscope which is: 1) reliable and easily used by a number of individuals; 2) has multiple exposure cameras; and 3) has excellent anticontamination facilities. In addition, a number of projects require quantitating large numbers of molecules and structures for statistical analysis (e.g., heteroduplexes, microtubule number and length); the dignitizer is requested for these projects.